Neisseria meningitidis can be serologically divided into at least 12 immunotypes (L1 through L12) based on its lipooligosaccharides (LOS). Some of meningococcal LOS mimic a human glycosphingolipid, paragloboside, in having lacto-N-neotetraose (LNnT, Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc) sequence as a part of the oligosaccharide structures of the LOS. We previously reported that eight of the twelve LOS types were bound an LNnT- specific monoclonal antibody (anti-My-28). The expression of the antibody- reactive epitope in the LOS was influenced by growth conditions and the LNnT epitope could be masked at the nonreducing end by sialic acid which was identified as N-acetyl-neuraminic acid (NANA). We have further investigated the linkage between the sialic acid and LNnT using linkage- specific lectins, Maackia amurensis agglutinin (MAA, for sialylalpha2- >3Gal..) and Sambucus nigra agglutinin (SNA, for sialylalpha2->6Gal..). Six of the eight LNnT-antibody reacting LOS bound MAA lectin but not SNA lectin indicating that NANA is alpha2->3 linked to LNnT sequence in the LOS. Therefore, many N. meningitidis LOS mimic human glycosphingolipids, paragloboside and sialoparagloboside (NANAalpha2->3paragloboside), in having in the same oligosaccharide sequences in their structures. The presence of these sequences in the LOS may play a role in the virulence of N. meningitidis by enabling the organism to evade host immune defenses.